1. Field of the Invention
This invention relates to the art of exhibiting variations of a set of data values on a two coordinate display by shaded contouring. The method is particularly applicable to data that is inherently lineated in one coordinate and which has been sampled at regular intervals along the other coordinate.
2. Discussion of the Prior Art
In the well-known practice of seismic exploration using the reflection technique, an acoustic wave is generated at regularly-spaced stations along a line of survey. The travel times of the acoustic waves from the respective generating stations at the surface to the subsurface rock layers are measured. The measured travel times are then plotted on a two-dimensional display as a function of travel time (or depth) along the vertical axis and as a function of horizontal distance of the generating stations or shot points along the horizontal X axis corresponding to the line of survey. The display may be plotted as a variable density, variable area or wiggle-trace section. Shading or colors may be superimposed on the display to further emphasize relative signal amplitues, frequencies, or both. The display represents a cross section of the earth showing the structural attitudes of the subsurface rock layers. The structure of the layers is an extrinsic parameter of the layers. That is, the inherent properties of the rock layers are not substantially altered by the structural attitude of the layers.
In order to properly interpret the structural section, other important attributes of the rock layer must be known such as the porosity and fluid content. These attributes can be deduced from knowledge of certain intrinsic properties of the rock layers, such as the acoustic interval velocity, acoustic attenuation and acoustic impedance. Accordingly, the structural section is often supplemented with a cross section showing the variations of a selected intrinsic rock property as a function of reflection time or depth. Typically the inherent rock properties tend to be highly lineated and consistent along the X coordinate. That is, the function describing the inherent rock property varies slowly along the X coordinate but it may change relatively rapidly in the vertical direction along the Y axis.
A visual display of lateral trends and variations of an exemplary lineated rock property may be enhanced by contouring and shading. Such contouring may be, and often is, done by hand or it can be automated. Automated contouring programs generally fit a curve, such as a cubic spline curve, to the data. In such a process all of the data values within a specified zone are considered even though some or many of the data values may be erroneous due to noise contamination of the original signal.
Usually the lineations are relatively thin along a vertical depth scale. Because undue weight tends to be applied by the contour program to erratic data values, the displayed lineations tend to become blurred at their upper and lower boundaries. The overall display lacks resolution across lithologic units. One type of such a cross section is illustrated on page 18 of the January, 1979 issue of Geophysics, published by the Society of Exploration Geophysicists, Tulsa, Oklahoma.